Chapter 19: Positron Emission Tomography in Heart Disease
Although the assessment of coronary flow and coronary flow reserve (CFR) is based on absolute rather than relative measures of myocardial perfusion, these measures may still appear reduced in the absence of obstructive epicardial coronary artery disease. Which of the following factors may lower stress perfusion to erroneously low ischemic levels?
C. Inadequate vasodilator stress
The answer is E. (Hurst’s The Heart, 14th Edition, Chap. 19) Caffeine, beta-blockers, inadequate vasodilator stress, and diffuse or small-vessel disease may lower stress perfusion in cc/min/g to apparently low ischemic levels; therefore, concurrently measuring rest flow and CFR provides integrated diagnostic information for correct clinical interpretation from the coronary flow capacity map.
The radioligand 18F-FDG is the most important and most widely used for the noninvasive study of the myocardium substrate’s metabolism with PET. In which of the following cells does 18F-FDG not trace glucose utilization?
A. Mechanical heart valves
The answer is A. (Hurst’s The Heart, 14th Edition, Chap. 19) As a glucose analog, 18F-FDG tracks the initial transport of glucose from blood into cells and its phosphorylation to glucose-6-phosphate as the initial metabolic step of transformation of exogenously derived glucose. Because phosphorylated 18F-FDG cannot be metabolized further, it is metabolically trapped in the cell, and it accumulates in tissue in proportion to rates of exogenous glucose utilization. However, the radiotracer 18F-FDG is not cell specific for myocardium. It also traces glucose utilization in different organs, such as skeletal muscle and brain, as well as in tumors and inflammatory processes. While 18F-FDG traces glucose utilization around prosthetic heart valves in cases of perivalvular infection, there is no utilization to trace within inert materials such as mechanical valve discs. Therefore, 18F-FDG is clinically useful for imaging regional myocardial metabolism and for identifying inflammatory disease of the cardiovascular system
Adequate patient preparation during the 24 hours before a 18F-FDG PET scan is essential for reliable results due to the myocardium’s ability to shift its energy needs among several fuel substrates, including free fatty acids, glucose, and lactate. Which of the following parameters does not affect the myocardium’s selection of fuel substrates?